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Hot Rods 12v Shock?

Discussion in 'The Hokey Ass Message Board' started by oj, May 23, 2018.

  1. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Here's an odd one, when you push the 'horn ring' to toot the horn and touch the metal part of the steering wheel you get a shock!
    I wired the car myself and the horn ring makes 'ground' for the horn relay. This is a fresh build (a '64 Tiger) and we're just now debugging, the engine isn't running quite right at idle (pertronix) and I'm wondering if, somehow, I'm getting a secondary voltage short thru the system. It is a Lucas engineered system with 2 circuits for the whole car.
    Any other theories, how do you get shocked from 12v DC?
     
  2. tubman
    Joined: May 16, 2007
    Posts: 6,916

    tubman
    ALLIANCE MEMBER

    I had the same problem with a '57 MG Magnette I had years ago. It'll be interesting to see what causes this.
     
  3. greybeard360
    Joined: Feb 28, 2008
    Posts: 2,074

    greybeard360
    Member

    Does the horn honk?
    Sounds like it is trying to ground thru you and not where it is supposed to.
     
    fauj and prewarcars4me like this.
  4. 73RR
    Joined: Jan 29, 2007
    Posts: 7,175

    73RR
    Member

    Lucas...the God of Darkness....
    Lucas used to make refrigerators and now the reason why Britons drink warm beer.:p

    12v is really not enough to be felt as a shock so me thinks there is some feedback loop from the coil/ignition.
    Replace the pertronix with the old points and see what happens.

    .
     
    OahuEli, loudbang, Kan Kustom and 5 others like this.

  5. What 73RR said
    12 v should not be felt, check your horn ground

    Unless your engine ground is shitty and the ignition is ground through the column


    Thought the brits didn’t make refrigerators as they could not devise a way for them to leak oil!
     
  6. 42merc
    Joined: Dec 19, 2010
    Posts: 894

    42merc
    Member

    I have experienced the same horn ring shock on a six volt system.
    The horn ring ground path is not clean.
    Make the metal under the ring bright & shiny.
     
    zuke likes this.
  7. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Guess what, no matter what I do it will not shock you unless the engine is running! I've got a Fluke87, I think it'll capture the voltage spike if I can figure which buttons to push on it.
     
    lothiandon1940 likes this.
  8. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    oscilloscope would be handy. Does an 87 have a scope feature? :)

    but check the grounds on the engine and column....and coil...
     
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  9. seb fontana
    Joined: Sep 1, 2005
    Posts: 8,444

    seb fontana
    Member
    from ct

    We call Lucas Prince of Darkness..Yeah, no help..
     
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  10. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    Must be a thing with Sunbeams mine wouldn't honk until the metal horn ring came in contact with the metal part of the steering wheel and yes there was a spark.
     
  11. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Does the column have the same potential ground as the battery? Verify in ohms.

    So for those who don't think 12 volts will shock you, please realize it's the current (amps) that will do it, not the voltage. I agree, it's usually not an issue, but potentially can be.
     
    Hnstray likes this.
  12. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
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    I think I'd put a condenser on the horn, connect the condenser wire to the horn terminal, and ground the condenser body. It may be that the shock you are getting is the field collapsing on the windings in the horn, similar to what an ignition coil does. Couldn't hurt to try it.....

    No matter the voltage, you don't have any current unless there is conductivity. In the case of getting a shock your body is the conductor. It's a damn poor one, and you need to be pretty sweaty for your body resistance to be low enough to generate enough current to feel with a 12 volt EMF.
     
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  13. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    but if you stick the terminals of a 9v battery on your tongue, you'll sure feel it!

    I can touch both terminals of a 12v battery, that is capable of producing hundreds of amps, and not feel it.

    It's interesting...
     
    belair likes this.
  14. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
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    I agree on both of your points, but that wasn't my point:)
     
  15. blowby
    Joined: Dec 27, 2012
    Posts: 8,661

    blowby
    Member
    from Nicasio Ca

    Weird. Now if you could get it to shock the driver of the car your honking at, that would be useful.
     
  16. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
    ALLIANCE MEMBER

    Saliva is saline, and the distance between the terminals is short on a 9v battery, so there is a current flow of about 3-4 ma, enough to feel, and kind of unpleasant. The upper layers of your skin are relatively dry (unless you're drenched in sweat which is also saline) and a much poorer conductor which is why you don't normally feel anything when working with live 12 volt circuits.

    Put 12 volts on a 9 volt battery pigtail and touch that to your tongue. That's a real treat!
     
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  17. R Pope
    Joined: Jan 23, 2006
    Posts: 3,309

    R Pope
    Member

    A 12 v battery won't shock you by itself, but if there is a poor connection making and breaking a circuit the current will flow through you when the circuit breaks. I guess the electrons, once moving, don't like to stop!
     
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  18. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    that does not make sense.
     
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  19. sunbeam
    Joined: Oct 22, 2010
    Posts: 6,214

    sunbeam
    Member

    Electricity flowing through a wire creates a magnetic field stop the flow and the field collapses through the wire creating a voltage spike much higher than the orginal voltage.
     
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  20. squirrel
    Joined: Sep 23, 2004
    Posts: 55,942

    squirrel
    Member

    In the context of this problem, yes, there likely is a situation where the circuit is being made and broken repeatedly, causing the shock. It's the primary side of the ignition system. There's a coil involved, though...and it's acting like an AC circuit.
     
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  21. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    Well, after much testing and wailing the piss out of it with a hammer I have concluded that it is, indeed, and electrical problem and not associated with the ignition. I disconnected the coil. The voltage is 13v from horn ring to steering wheel/column. The resistance from steering wheel/column to ground at the relay is .1ohm; from steering wheel/column to engine ground is .6ohms
     
  22. KenC
    Joined: Sep 14, 2006
    Posts: 1,045

    KenC
    Member

    Yep, the most painful shock I've had was from a 12v battery. Hot day, sweating like a pig, short sleeve shirt, removing the starter from a car. I leaned over the battery, like a dummy I didn't remove the ground cable. Sweaty arm on the neg post, wrench on the hot post of the starter solenoid. Arm just cramped up and twitched like a frog on a lab table. Hurt for hours.
     
  23. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    Most multi-meters are not accurate at measuring that low of resistance. Not sure how much trust I would place on your resistance measurements unless you have a very accurate (very expensive) precision ohm meter.

    https://en.wikipedia.org/wiki/Ohmmeter
     
  24. Ebbsspeed
    Joined: Nov 11, 2005
    Posts: 6,250

    Ebbsspeed
    ALLIANCE MEMBER

    A horn is very similar to a coil, in that it is many turns of wire around a metal core, and includes a set of points that break when the coil is energized and the horn diaphragm is pulled towards the electromagnetized core. When the points break, the field collapses, the diaphragm is released, the points close, and the process repeats itself, at the same frequency as the audio frequency of the horn. Almost like a Model T buzz coil primary winding circuit, isn't it?
     
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  25. oj
    Joined: Jul 27, 2008
    Posts: 6,454

    oj
    Member

    The ground is just for the relay coil, it isn't carrying the horn load at all, it'll see maybe 60 milliamps? I do see what you are saying and agree but the horn business should be totally seperate from the relay coil. The horn relay has a common 12v feed for both horn and relay coil, the horn ring provides the ground for the relay coil and completes the 12v circuit to the horn relay, the relay closes and completes the +12v to the horns, the horns are grounded seperate from the horn relay - physically seperate.


    Fluke 87
     
  26. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,681

    Bruce Lancaster
    Member Emeritus

    I had this for a while after rewiring my '48 Ford. In my case I had the two smaller wires on the battery relay swapped...
    I am pretty sure this is more than just you becoming part of the ground circuit...the shocks I experienced were pretty clearly high voltage, nearly lifting me off the seat. I think the coil within the relay is entering the circuit to step up the voltage just as an ignition coil does.
     
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  27. Atwater Mike
    Joined: May 31, 2002
    Posts: 11,625

    Atwater Mike
    Member

    Inertia, Squirrel. Like when a 'talker' is rambling. Verbel inertia makes it hard to shut him up.
     
  28. Budget36
    Joined: Nov 29, 2014
    Posts: 13,174

    Budget36
    Member

    Take a look at this video, I know this will extend the life of the contacts, but could possibly be a source of your problem?

     
  29. Atwater Mike
    Joined: May 31, 2002
    Posts: 11,625

    Atwater Mike
    Member

    Shocking that anybody would use Lucas electrics.
     
  30. Blues4U
    Joined: Oct 1, 2015
    Posts: 7,589

    Blues4U
    Member
    from So Cal

    As nice of a meter as that is, it's still not real accurate at <1 ohm. Sorry, I don't mean to be argumentative or degrade your meter, it's just that, and this is a common misconception out there, but a standard multimeter, even one as nice as the Fluke 87, just cannot measure that low of resistance with very great accuracy. It takes a specialized precision ohmmeter with 4 leads using a different process to accurately measure very low resistance, something like this: http://www.bkprecision.com/products/electrical-battery-testers/310-digital-milli-ohm-meter.html

    I just think you may end up on a wild goose chase if you're trying to diagnose a problem looking at differences in resistance below 1 ohm. For probably everything you'll ever need for working on a car that kind of accuracy is not necessary.
     

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